1. Field of the Invention
The present invention provides aluminum bronze glassmaking molds. The molds of the present invention allow for efficient rates of glass forming and exhibit excellent physical characteristics.
2. Description of the Prior Art
While glassmaking is an ancient art, modern glassmaking can be traced to Ingle, U.S. Pat. No. 1,911,119, the content of which is hereby incorporated by reference. The conventional Hartford Individual Section glassware forming machine, such as disclosed in U.S. Pat. No. 1,911,119, may be of the "press and blow" type, exemplified by Rowe, U.S. Pat. No. 4,002,454, the content of which is hereby incorporated by reference, or of the "blow and blow" type, exemplified by Nebelung et al., U.S. Pat. No. 4,009,018, the content of which is also hereby incorporated by reference. Cf. Nebelung et al., U.S. Pat. No. 4,070,174, and Braithwaite, U.S. Pat. Nos. 4,222,761 and 4,222,762.
Both types of the Hartford I.S. glassware forming machine require the glassmaker to use a myriad of individual molds for the numerous molded sections. Such sections include blanks, molds, neck rings, plungers, blowheads, finish sleeves, baffles and bottom plates in both "press and blow" and "blow and blow" types; the dummy guide ring, dummy sleeve, and funnel unique to the "blow and blow" type; and the plunger head, baffle body, and baffle insert unique to the "press and blow" type.
Cast iron, being inexpensive, easy to machine, and widely available, was used extensively as the mold material for each of the aforementioned molds. However, its low wear resistance due to low hardness, tensile and yield strengths, low resistance to oxidation, and tendency to thermal cracking cause cast iron to fail under the severe operating parameters of modern Hartford I.S. glass forming. These operating parameters partially result from the desire of the glassmakers to form the glass much faster than in the original Hartford I.S. glass forming technique.
The rate of glass forming is a function of the thermal conductivity of the mold from which each individual glass section is produced. Even apart from its other shortcomings, cast iron is not suitable for many glass molding sections as, at a thermal conductivity of approximately 24-27 B.t.u./hr/ft.sup.2 /ft/.degree.F. at 850.degree. F., it either draws too much heat from the glass too quickly (i.e., its thermal conductivity is too high), or too little heat too slowly (i.e., its thermal conductivity is too low), and thereby causes glass forming difficulties with many individual glass sections.
The establishment of an optimum glass forming rate requires that the thermal conductivity of the mold of each individual section be carefully circumscribed. For example, the bottom plate and neck ring in "blow and blow" molding should be produced in molds characterized by a thermal conductivity of about 25-37 B.t.u./hr/ft.sup.2 /ft/.degree.F. at 850.degree. F. while "blow and blow" finish guide plates or "press and blow" plungers should be molded in low thermal conductivity environments, i.e., from 18-20 B.t.u./hr/ft.sup.2 /ft/.degree.F. at 850.degree. F.
Prior art nickel-boron or stainless steel alloys that exhibit good wear resistance and low thermal conductivity are difficult to machine and too expensive for wide commercial application. The thermal conductivities of the aluminum bronze alloys disclosed in U.S. Pat. Nos. 3,258,334 and 3,405,015 are too high for many glass sections, resulting in glass forming difficulties. Commonly used cast aluminum bronzes, having the nominal chemical composition of 15% nickel, 10% aluminum, 9.0% zinc, 0.5% iron, 0.2% manganese, 0.2% lead, and the balance copper, suffer from pitting corrosion due to sulfur in the swab dope preferentially corroding the copper-zinc rich phase, and from the zinc leaving the microstructure of the alloy at elevated temperatures. The lead in such alloys also contributes to the pitting corrosion. Further, such alloys thermal conductivity of approximately 38.0 B.t.u./hr/ft.sup.2 /ft/.degree.F. at 850.degree. F. is again too high for most glass sections.
Another prior art aluminum bronze alloy employed in glass molds has a chemical composition as follows: 9-9.5% aluminum, 4.5-5% nickel, 4-4.5% iron, and the balance copper. This alloy is reported to suffer from reduced wear resistance, and a thermal conductivity essentially equal to cast aluminum bronzes.
Also used for glass molds is an aluminum bronze with a nominal chemical composition of 7.80% aluminum, 4.21% nickel, 5.41% iron, 1.20% manganese, 0.06% silicon, and the balance copper. This alloy suffers from low strength and poor pitting resistance, and its thermal conductivity of approximately 36 B.t.u./hr/ft.sup.2 /ft/.degree.F. at 850.degree. F. is too high for most glass sections.
Thus, it can be seen that the various glass molding materials of the prior art suffer from a variety of drawbacks. The lack of durable, cost-effective, easily maintained, wear and pitting corrosion resistant molds with a variety of low-to-moderate thermal conductivities at elevated temperatures, prevents the rapid glass forming required by modern glassmaking. Further, the prior art's use of a wide variety of metallurgically diverse alloys exacerbates the cost and difficulty involved in maintaining the various equipment needed to machine and repair the myriad molds utilized in a Hartford I.S. glass forming apparatus.
Therefore, it is an object of the present invention to provide a series of aluminum bronze alloyed molds for use in the molding of individual sections in glassmaking processes.
It is also an object of the present invention to provide a series of glass molds produced from aluminum bronze alloys that exhibit a wide variety of low-to-moderate thermal conductivities at elevated temperatures.
It is also an object of the present invention to provide a series of aluminum bronze molds that allow efficient glass forming in glassmaking processes.
It is a further object of the present invention to provide a series of aluminum bronze molds that have excellent wear and pitting corrosion resistance, are durable, and are particularly suited for the hot-end molding of glass.
It is another object of the present invention to provide a series of aluminum bronze alloy molds that are substantially free of zinc and lead and are particularly suited for glass molding in a Hartford I.S. type glass forming machine.
It is also an object of the present invention to provide a series of aluminum bronze alloy molds that may be easily machined and repaired.